1. Field of the Invention
The present invention is directed to a method for switching from a first operating condition of an integrated circuit to a second operating condition of the integrated circuit differing from the first operating condition, particularly with respect to an integrated sensor.
2. Description of the Related Art
Many integrated circuits implement a specific operating condition/behavior (a xe2x80x9ctest modexe2x80x9d) for better testability; this behavior allows conclusions to be made about functions of the circuit that are difficult to measure from the outside. In order to avoid using a separate signal input for the transmission of the test mode information, but while managing with existing terminals already occupied with functions, a way must be found to make a specific signal or a combination of a plurality of signals available to the integrated circuit such that they differ from those of the normal operating case.
A functionally simple solution for distinguishing between normal and test mode is to apply a maximum voltage that is usually forbidden in the normal operating case to a circuit input and to internally recognize this voltage level with a comparator. However, this solution is disadvantageous in that the full range of voltage cannot be made available for operation; furthermore, the comparator consumes power.
Another possibility for distinguishing between normal and test mode involves transmitting the information by modulating the voltage at a circuit input and internally evaluating this modulation with a suitable circuit. The realization and communication of this protocol, however, requires greater outlay, and also requires additional power consumption.
The present invention is therefore based on the object of offering a method for switching between two different operating conditions of an integrated circuit that largely reduces or avoids these difficulties.
This object is achieved by the method and appertaining apparatus for switching from a first operating condition of an integrated circuit to a second operating condition of the integrated circuit differing from the first operating condition as described below. Further advantageous embodiments, developments and aspects of the present invention are also provided.
Inventively, a method for switching from a first operating condition of an integrated circuit to a second operating condition of the integrated circuit differing from the first operating condition is provided in which the integrated circuit generates a prescribed output voltage as an output signal at least in the first operating condition and at least one circuit output. The inventive method comprises the steps:
a) the integrated circuit is placed into the first operating condition;
b) the circuit output is externally charged with a voltage that differs from the prescribed output voltage;
c) the voltage present at the circuit output is evaluated; and
d) the integrated circuit is placed into the second operating condition dependent on the evaluation in step c).
This object is also achieved by an integrated circuit having a circuit arrangement for switching from a first operating condition of the integrated circuit to a second operating condition of the integrated circuit differing from the first operating condition. This integrated circuit generates a prescribed output voltage as an output signal at least in a first operating condition and at least one circuit output, and the circuit arrangement for the switching comprises at least one evaluation unit that is connected to the circuit output of the integrated circuit and comprises at least one control unit that is connected to the evaluation unit and generates at least one control signal dependent on the result of the evaluation unit such that the integrated circuit switches from the first operating condition into the second operating condition.
The inventive method and/or the inventive integrated circuit have the advantage that the switching from one operating condition into another operating condition of the integrated circuit can be implemented in a very simple way but with a high immunity to interference. As needed, the switching can be very easily initiated because the only thing needed for this is the application of a voltage level that is already available in the system to an output of the integrated circuit. Furthermore, the selection of a circuit output assures with a high certainty that the switching condition will not accidentally occur, since this is largely precluded by the usual, external interconnection of a circuit output. At the same time, the evaluation of the voltage adjacent at the circuit output can be implemented with a relatively simple circuit-oriented mechanism and can be implemented in a largely low-power or power-free manner.
According to a preferred embodiment of the inventive method, the prescribed output voltage corresponds to a logical value and the voltage externally applied to the circuit output corresponds to the logical value complementary to said logical value. This embodiment has the advantage that the evaluation of the voltage adjacent at the circuit output can be implemented nearly power-free with especially simple evaluation units, particularly logical operations. It is particularly preferred when the logical value that corresponds to the voltage adjacent at the circuit output is logically operated with the logical value that corresponds to the prescribed output voltage using an XOR operation or using a NOR operation.
According to another preferred embodiment of the inventive method, the integrated circuit is placed into the second operating condition when the voltage adjacent at the circuit output does not coincide with the prescribed output voltage over a prescribed time span. This prescribed time span has the function of internally declaring the switching valid only after this condition has existed for a certain length of time, which further enhances the immunity to interference.
According to another preferred embodiment of the inventive method, the integrated circuit is placed back into the first operating condition when at least one prescribed criterion is met. For example, the integrated circuit can be reset after a predetermined time following the beginning of the second operating condition. This resetting after the expiration of a predetermined time interval, however, is only one of many possibilities for the resetting. For example, the integrated circuit can also be in turn reset after a renewed application of the operating voltage. Further possibilities may include introducing a separate reset command or utilizing other, inherently forbidden over-voltages and under-voltages. Instead of being placed into the first operating condition given the presence of a prescribed criterion, the integrated circuit can also be placed into a further (third, fourth, etc.) operating condition.
According to a preferred embodiment of the inventive integrated circuit, the evaluation unit comprises at least one logic circuit, particularly an AND or a NOR circuit. It is especially preferred when the evaluation unit comprises simple AND or NOR gates.
According to another preferred embodiment of the inventive integrated circuit, the control unit comprises a memory. After a positive result of the evaluation, the evaluation unit can store this condition in the memory until the memory is reset due to the presence of a further criterion and, thus, the integrated circuit is placed back into the first operating condition (or into some other operating condition).
According to another preferred embodiment of the inventive integrated circuit, the circuit arrangement for the switching comprises at least one time-counter unit. Such a time-counter unit can assist in implementing a prescribed time span over which the voltage at the circuit output must not coincide with the prescribed output voltage so that a switching can ensue.
According to another preferred embodiment of the inventive integrated circuit, the circuit arrangement for switching comprises at least one monitoring unit. The monitoring unit serves the purpose of checking the at least one criterion on the basis of which a decision is made as to whether the integrated circuit is reset into the first operating condition.